EMERY (Fr. emeril, Ger. schmergel, Gr. smiris; allied to smear), a variety of corundum (q.v.), or of the same mineral species of which corundum and sapphire (with oriental ruby, etc.) are also varieties. It agrees with them very perfectly in composition, hardness, and specific gravity; but is dull, opaque, and not crystallized, sometimes of a grayish black, and sometimes of a blue color. It occurs both massive and disseminated. Its masses, although very compact, have a somewhat granular structure. It is found in several parts of Europe, in Asia Minor, Greenland, etc., generally in masses scattered through aqueous deposits, but in one locality in Saxony in beds of steatite in a schistose rock. The E. of commerce is chiefly obtained from the island of Naxos. Being very hard, it is much used for grinding glass and polishing metals and other hard substances. It is found in lumps, having a granular structure. It is composed of alumina, oxide of iron, and silica, with a little lime, in proportions varying considerably with different specimens. The following may be taken as an average: alumina, 82; oxide of iron, 10; silica, 6; lime, 14.
It is prepared for use by first breaking it into lumps about the size of a hen's egg, then crushing these to powder by stampers. It is then sifted to various degrees of fineness, which are numbered according to the meshes of the sieve. Plate-glass manu facturers and others separate E. powder into different degrees of fineness by the method of elutriation (q.v.). A number of copper cylinders of graduated capacities are placed in a row, and filled with water; the E., churned up with an abundance of water, is admitted by a pipe into the smallest, it then passes to the next in size, and finally flows from the largest; and thus, as a given quantity of water with E. suspended in it, passes in equal times through vessels of varying capacities, the amount of agitation will obviously be greatest in the smallest vessel, least in the largest, and in like proportion with the intermediate; the largest particles, therefore, sink in the smaller vessel, and so on till only the very finest will reach the largest vessel. In this manner, any number
of gradations of fineness may be obtained, according to the number and sizes of the vessels. Elutriation in oil or gum-water is sometimes used on a smaller scale, the E. being stirred up in the liquid, and portions poured off at different intervals of time, the finest being, of course, the last to settle. The use of the oil or gum is to make the subsidence take place more slowly.
E. thus prepared is used for a great many important purposes in the arts. Being next in hardness to diamond-dust and crystalline corundum, the lapidary uses it for cutting and polishing many kinds of stone. Glass-stoppers of all kinds are ground into their with it. Plate-glass is ground flat by its means; it is also used in glass cutting, and in grinding some kinds of metallic fittings. When employed for the polishing of metals, it has to be spread on some kind of surface to form a sort of fine rile. E. paper, B. cloth, E. sticks, E. cake, and E. stone, are various contrivances for such purposes.
E. paper is made by sifting E. over paper which has been covered with a coating of glue. It is used either by wrapping it round a fine file, or a stick, or in the hand, according to the form of the work. See POLISHING OF .31ETAI,S, E. cloth is made like E. paper, with coarse calico substituted for the paper. The E. does not adhere so well as to paper, and it is therefore not used by metal-workers, who work E. paper till smooth with wear, but is chiefly used for purposes where the hand alone is used, and Would teart,Foitized by Microsort E. sticks are used for the same purposes as E. paper wrapped round files; they are made of deal sticks shaped like files, then glued over, and dipped once or twice in a heap of emery.
E. cake is a compound of bees-wax, suet, and E., melted and well worked together. It is applied to buffing wheels, etc.
E. stone is a kind of earthenware mixed with E., formed by pressing a mixture of clay and E. into suitable molds, and then firing, like common earthenware. It is molded into wheels, laps, etc. Its hardness and cutting power are very considerable.